This invention relates to arthroscopic surgery of the temporomandibular joint (TMJ) and methods and devices for incision, excision, repositioning, recontouring, and replacement of joint fluids and soft and hard tissues by "less invasive surgery" technique.
The temporomandibular joint (TMJ) is the freely movable articulation between the condyle of the mandible and the squamous portion of the temporal bone. While having much in common with other synovial joints of the body, there are several anatomic and functional characteristics that distinguish the TMJ from most other synovial joints. These distinctions are as follows:
(a) The articulating surfaces of the bones are covered by an avascular fibrous connective tissue that may contain a variable number of cartilage cells and thus can be designated fibrocartilage.
(b) The two articulating complexes of bone carry teeth, whose shape and position influence the movements of the joint. It is the only joint with a rigid end-point of closure.
(c) It has a bilateral articulation with the cranium, so the right and left temporomandibular articulations must function together.
(d) The TMJ is a complex joint because each joint has an articular disc (meniscus) interposed between the condyle and the temporal bone.
The TMJ is a combined hinge-glide articulation of the mandibular condyle with the mandibular fossa and articular eminence of the temporal bone. The muscles of mastication and the suprahyoid muscles act bilaterally to produce three types of movement: rotation, translation, and a combination of rotation and translation movement of the condyles. Rotation and some slight translation take place in the lower joint space between the condyle and the articular disc. Translation of the condyle-disc complex takes place in the upper joint space.
Changes in the disc-condyle relationship often produces pain and/or functional disturbances in the masticatory system. The disc is most commonly displaced anteromedially and, in the last few years, the term "internal derangements of the TMJ" connotes any disturbance between the articulating components within the joint proper.
Little is known about the prevalence of displacement. Some authors (W. L. McCarty, Jr. and W. Farrar: Surgery for Internal Derangements of the Temporomandibular Joint. J. Prosthet Dent 42:2 79) maintain that it is extremely common, whereas others believe it is rare. In a recent autopsy study of young adults, (W. Solberg, T. Hanson, B. Nordstrom: Morphologic Evaluation of Young Adult TMJs at Autopsy, abstracted J. Dent Res 63:228 1984), found disc displacement in 11.6% of the TMJs and noted it to be present more commonly in women. In other study of adult cadavers by P. L. Westesson and M. Rohlin, Internal Derangement Related to Osteoarthrosis in Temporomandibular Joint Autopsy Specimens, Oral Surg 57:17, 1984, disc placement was found in 56% of the TMJs. Thus, the prevalance of disc displacement appears to increase with age.
Persistent (chronic) "closed locking" of the temporomandibular joint has been attributed to internal derangement due to anterior disc displacement without reduction. Anatomic, arthrographic, clinical, and surgical studies have supported this concept. Among such studies is C. H. Wilkes: Structural and Functional Alterations of the Temporomandibular Joint. Northwest Dent 57:287, 1978 and C. H. Wilkes: Arthrography of the Temporomandibular Joint in Patients With the TMJ Pain-Dysfunction Syndrome. Minn Med 61:645, 1978.
The natural history of internal derangement leading to persistent "closed lock" has been described by V. E. Ireland: The Problem of "The Clicking Jaw". Proc. R. Soc. Med. 44:191, 1951 and M. F. Dolwick, R. W. Katzberg, C. A. Helms: Internal Derangement of the Temporomandibular Joint: Fact or Fiction? J Prosthet Dent 49:415, 1983. Trauma to the mandible has been reported to be a common etiologic factor leading to the development of internal derangement with closed lock. The traumatic event may result not only in disc displacement, but also intracapsular microbleeding and effusion. Subsequent adhesions may form. These adhesions are most commonly seen in the superior compartment. Additionally, morphological changes occur in the TMJ including synovitis and synovial hyperplasia.
Treatment of acute closed locking of the TMJ may include mandibular manipulation, splint therapy, and other non-surgical therapy. These modalities are intended to "recapture" the displaced disc. If "non-invasive therapy" is not successful, a persistent (chronic) closed lock may occur.
A plethora of evidence exists demonstrating the reality of disc displacement. This evidence includes clinical, anatomic, radiographic, and surgical findings. It has been shown that the TMJ disc is displaced anteromedially and that the displaced disc can mechanically interfere with jaw movement.
P. L. Westesson and M. Rohlin: Internal Derangement Related to Osteoarthrosis in Temporomandibular Joint Autopsy Specimens, Oral Surg 57:17, 1984, studying adult cadaver TMJs, have shown a progression of internal derangements that includes not only changes in disc position but also in disc configuration. A progression from oblique disc position with biconcave disc or disc of even thickness to complete displacement with biconvex disc configuration was shown. The most advanced form of internal derangement showed perforation of the disc and/or its attachment tissues. The occurrence of osteoarthrosis was observed to increase with more advanced disc displacement and changes in disc configuration. Discs of even thickness were associated with osteoarthrosis in 50% compared to 90% for biconvex discs.
The disclosures of the foregoing references are hereby incorporated by this reference.
Temporomandibular joint surgery via arthrotomy (open surgical approach) has been widely advocated for treatment of internal derangements with closed lock when non-surgical therapy has failed. Preauricular, endaural, and postauricular approaches have been employed by various clinicians. Disc repositioning, arthroplasty, meniscectomy with implant, and other procedures have been described to treat internal derangement.
However, one of the principal disadvantages of open surgical approach is that a relatively large incision is necessary to perform two basic procedures: disc repositioning and disc removal. Typically, a curvalinear incision of 6 to 7 centimeters is made and extended through skin and subcutaneous tissues to the depth of the temporalis fascia. The superior part of the flap is extended anteriorly by blunt dissection with a periosteal elevator. The flap is developed inferiorally adjacent to the external auditary cartilage. Usually, a vein crosses the lateral aspect of the articular fossa. This vein while identifying the correct depth of the capsule, is generally dissected out, clamped, divided, and ligated or cauterized.
An oblique incision, parallel to the temporal branches of the facial nerve, is typically made through the superficial layer of the temporal fascia. The incision may extend to bone over the lateral part of the fossa. Its inferior aspect generally should be no farther than 8 millimeters in front of the tragus of the ear. As before, the lateral aspect of the fossa is exposed by blunt dissection with a periosteal elevator.
This type of surgical procedure can lead to a relatively high complication rate, among other disadvantages. For instance, the serious dangers associated with TMJ surgery via arthrotomy include facial nerve paralysis with inability to close eyelid on the affected side, and inability to wrinkle the forehead, post-operative infection, resultant malocclusion (incorrect bite) and limited opening, lack of improvement or worsening of pain and jaw dysfunction; and further degenerative changes with the TMJ.
Accordingly, those skilled in the art have recognized a significant need for TMJ arthroscopic surgical treatment which affords the clinical advantages of using relatively small incision techniques, yet possesses the requirements thereby providing a safer and more convenient surgical procedure and more comfortable therapy for the patient.